View Full Version : Temp gauge dies, AC won't cool, Cooling fan is on max.....

09-23-2011, 09:14 AM
So I need some help figuring this one out.

This is the 3rd time my car has done this, sadly it couldn't do it while it was in warranty and had to wait till it was 100 miles out of warranty to start.

The issue is intermittent and never sets a SES code. When it happens it usually never lasts for more than an hour or two.

First indication is usually the coolant temp gauge reads 0 (needle is flat as if ignition/engine is off), but whenever this happens the following is also true. The AC clutch won't engage, and the cooling fan is at max speed (variable fan).

My thoughts are the CTS, or its connector is perhaps bad, or a common ground between the 3 systems is bad. The Coolant gauge in the car probably gets a signal from the PCM. I don't have a scan tool to see what the PCM is reading for coolant temp.

Though if coolant temp was reading in the negative due to a bad sender or poor connection I would think the PCM would set a SES code, and and perhaps the PCM commands max fan because it doesn't know what the engine temp is so it acts like a fail safe?

With my luck on my way over to autozoo or something the issue will disappear and I won't be able to track it down.

09-23-2011, 09:29 AM
Found a similar issue here, though no mention of AC issues with it.

And again here yet another one. Though this one says that the Thermostat can cause this issue if it gets stuck open. But even stuck open the engine should still generate enough heat to at least register on the gauge. Also his has a code, I have no SES light. Which is strange. You'd think something like this would throw a code.

09-23-2011, 06:42 PM
And once again the issue has fixed itself with no sign of why it broke.

09-23-2011, 10:33 PM
Need to go thru the cars modules & see if something is pissing it off.
Some of those fuctions your losing are part of the GM LAN data buss.
PCM is not the master here.
This is a series parallel data buss vehicle.
The BCM is the master.
VCIM (vehicle commincation interface module) controls the series communication leg of the buss. Including the PCM & IPC (cluster).
The gauge acting funny is a clue, as is no A/C & fan on full speed.
The fan is a 2 speed hi/low.

The PCM controlls the relays to the A/C clutch, & the cooling fan relays.
Need to hook up a real scan tool to your car, not OBD-II that's useless here.
The PCM may still contain some infomation on the GM/OEM data side as well as other modules in the network.

Josh 94Z
09-24-2011, 10:00 AM
This is interesting. A coworker just had the identical thing happen this week in his Saturn Aura. He also noted that it felt like it had pulled all the timing and was in some kind of limp mode. The SES light was not on, but when he hooked up his scan tool, it showed a pending code. I don't remember the number, but it was something like a temperature mis-match? Clearing the code immediately remedied the problem (the gauge read normal, A/C worked, and the fan returned to normal).

My initial suspicion would be one of the coolant temp sensors or a dirty connection.

I do know with a stuck thermostat that you can get a code, though. My Honda Civic had that issue, and it will set a code if the coolant temperature does not rise to a certain point above the IAT in an alloted time.

09-26-2011, 01:51 PM
Well, it just happened to do it on the way to Tim's house yesterday when I was like 5 minutes from an Autozone. I drove by got it scanned.

P0128 I think it was, basically relating to an issue either with the CTS, Stat, or low coolant.

The issue went away on its own later, but I changed the CTS anyways. Issue hasn't reoccurred yet, but sometimes takes weeks to happen. We shall see if its fixed. If not, I'll replace the Stat next.

09-26-2011, 09:36 PM
Well that would be great if it is the stat....
I be honest dont see a lot of CTS's nowadays though.
It has to be electrical though, not a t-stat.

09-26-2011, 11:08 PM
Not really, but the code lists only 3 possible things and the CTS made the most sense from that. It wasn't that expensive so it was worth a check.